Furnace

ABSTRACT

A furnace wall is constructed with or includes coolers of the type comprising a main body made of cast iron or copper and a plurality of cooling tubes cast integral with the main body so that the furnace wall may be cooled by cooling water flowing through the cooling tubes. Water leakage problem may be overcome and the life of the furnace wall may be remarkably increased.

O United States Patent [191 [111 3,843,106 Nanjyo et al. Oct. 22, 1974 [54] FURNACE 1,948,696 2/1934 Brassert et al. .i. 266/32 [75] Inventors: Toshio Nanjyo; Masayuki Aoshika, 35:32: both Of Yokohama, Japan 2,686,666 1954 [73] Assignee: Ishikawajima-Harima Jukogyo 3:32? Kabushiki Kaisha, Tokyo, Japan 3:690:633 9/1972 [22] Filed: Apr. 17, 1973 3,706,343 2/1 2 [21] Appl. No.: 351,855

Prlmary Exammer-Gerald A. Dost Attorney, Agent, or Firm-Scrivener Parker Scrivener [30] Foreign Application Priority Data and Clarke Apr. 28, 1972 Japan 47-42912 May 30, I972 Japan 1 May 30, 1972 Japan [57] ABSTRACT Feb. 8, 1973 Japan 48-17032 A furnace wall is constructed with or includes coolers [52] U 8 Cl 266/43 266/32 of the type comprising a main body made of cast iron [51] F27d U12 or copper and a plurality of cooling tubes cast integral [58] Fieid B2 with the main body so that the furnace wall may be 7 cooled by cooling water flowing through the cooling tubes. Water leakage problem may be overcome and [56] References Cited the life of the furnace wall may be remarkably in- UNITED STATES PATENTS creased 5l5,085 2/1894 lles 266/32 7 Claims, 10 Drawing Figures SHEET 2 0| 5 PATENTEI] GET 2 2 1874 ale-43106 warm 5 PATENTEflnm 22 1914 lem.

FURNACE The present invention generally relates to a furnace.

The conventional steel making arc furnaces generally comprise a furnace shell made of steel plate and lined with refractory materials. The service life of the refractory materials or brick is generally 200 350 heats, and the furnace bottom and the slag line are repaired with stamping materials while they are hot whenever the molten metal is removed out of the furnace. Of the refractory brick of the furnace wall those at the hot spots which are directly exposed to the high temperature arcs have a shorter life of the order of 30 I heats. Since the steel making arc furnaces are recently operated at a high current and voltage in order to improve the productivity, the life of the furnace wall or refractory brick becomes much shorter, so that the cost is remarkably increased and the decrease in furnace operation efficiency due to the increase in time required for repair of the furnace wall and so on presents a serious prob- In order to overcome these problems there has been proposed a method in which a steel pipe type or welded-steel-plate jacket type cooler is placed in the furnace wall so as to cool the brick thereby increasing its life. But thismethod is not satisfactory because of the following reasons:

a. The brick laid in front of the cooler tends to fall off and the service life of the brick cannot be increased as expected.

b. In case .of the jacket type cooler, the brick in front of the cooler tends to fall off so that the cooler is exposed to the high temperature in the furnace. As a result water leakage through the welded joints tends to occur.

c. When the thick steel plates are used in the jacket type cooler and if they are exposed directly to the high temperature in the furnace, the cracks tend to be produced because of the temperature difference between the surface of the cooler exposed to the high temperature in the furnace and the surface cooled by cooling water. Therefore the maximum allowable thickness is of the order of 9 l2 mm so that a hole is most frequentlyformed through the steel plate due to the spark between the steel plate and scrap in the melting stage and cooling water leaks through the hole.

(I. The jacket type cooler is made of thin steel plates which are welded together. The inner surface of the cooler is generally flat so that it is difficult for splash to adhere to the surface. As a result the surface is directly exposed to the arcs so that a large quantity of cooling water is required and the heat flux density is increased to the order of 600,000 Kcal/m h. Therefore the thermal efficiency of the furnaceis remarkably reduced and the life of the cooler is also decreased.

Even when the coolers are placed in the furnace wall, the construction of the coolers presents the problems of reduction in thermal efficiency of the furnace and of water leakage as described above so that the inherent problems of the furnace cannot be solved at all.

Furthermore the increase of the life of the furnace wall by the selection of the refractory materials available at present is limited.

One of the objects of the present invention is therefore to provide a furnace whose furnace wall has a long life and which may improve the furnace operation efficiency thereby reducing the operational cost.

Another object of the present invention is to provide a furnace whose furnace wall may be prevented from being locally damaged so that its life may be increased.

Another object of the present invention is to provide a furnace in which all of the furnace wall may be cooled so that the life of the furnace wall may become semipermanent, thus resulting in the reduction in time required for maintenance and repair.

Another object of the present invention is to provide a furnace in which the hot spots of the furnace wall are spacedapart from the electrodes as far as possible so that scrap may be uniformly melted and the damages to the furnace wall may be made uniform.

Another object of the present invention is to provide a furnace in which a furnace roof may be made small in size and light in weight so that the quantity of brick required for the construction of the furnace roof may be minimized, thus resulting in the reduction in cost.

Another object of the present invention is to provide a furnace which are constructed with coolers which have a long service life and whose thermal loss is less so that the life of the furnace wall may be increased.

Briefly stated according to the present invention a furnace comprises a hearth constructed by the conventional method with refractory brick and stamping material and a furnace wall constructed with coolers each comprising a main body made of cast iron or copper and a length of cooling tube cast with the main body.

The lowermost coolers are spaced apart from the surface of molten steel by a length of 200 500 mm so that the adhesion of molten steel to the surfaces of the coolers may be prevented. The service life of the furnace wall may be increased by cooling it with water, and the water-tightness of the furnace wall may be ensured. More particularly cooling water flows through the cooling tubes in the coolers so that the furnace wall may be always cooled. The abrasion and wear of the furnace wall may be minimized so that the service life may be increased and the efficiency may be remarkably improved.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof taken in conjunction with the accompanying drawing:

FIG. 1 is a front view of a cooler used in the furnaces in accordance with the present invention;

FIG. 2 is a sectional view thereof;

FIG. 3 is a front view of another example of a cooler used in the furnaces in accordance with the present invention;

FIG. 4 is a sectional view thereof;

FIG. 5 is a fragmentary sectional view of a first embodiment of a furnace in accordance with the present invention;

FIG. 6 is a sectional view of a second embodiment of a furnace in accordance with the present invention; and

FIGS. 7, 8, 9 and 10 are cross sectional views of a third, fourth, fifth and sixth embodiments of the present invention.

According to the present invention the coolers of the type shown in FIGS. 1-4 are used.

in the horizontaldirection and beyond the side surfaces thereof. The adjacent cooling tubes are communicated with each other at their ends and the free end of the lowermost cooling tube 2 is used as an inlet 3 whereas the free end of the uppermost cooling tube 2 is used as an outlet 3: The inner surface of the cooler I is corrugated as best shown'in FIGS. 5 and 6 in such a manner that the portion corresponding to the cooling tubeis converged outwardly.

Next referring to FIGS. 3 and 4, a cooling block or cooler I, is substantially similar in construction to that shown in FIGS. 1 and 2 except that a plurality of refractorybrick 5 are cast integral with the main body 1 of the cooler l in vertically spaced apart relation in such a manner that their ends may be exposed at the inner surface of the main body 1'.

When the coolers or cooling blocks I and I of the types shown in FIGS. 14 are used, the water leakage as well as the decrease in thermal efficiency may be mine the average temperature of the atmosphere in the furnace and the combined coefficient by conduction,

convection and radiation.

prevented. The cooler I has the corrugated inner surface and the outwardly diverging portion is formed coaxially of the cooling tube so that the uniform cooling effectmay be attained. Therefore the crack due to the thermal stresses which in turn are caused by the difference in temperature in the cooler may be prevented. Even if the crack is started the water leakage may be prevented because the cooling tubes are cast integral with the main body. Furthermore the adhesion of splash to the corrugated inner surface 5 may be improved so that a protective wall or layer may be formed. Therefore the thermal loss and the decrease in thermal efficiency may be prevented.

'As described above the thickness of the cooler block I or I" must be so selected that the temperature of the inner surface is less than the melting point of the cooler and the solidification point of the molten metal in the furnace. The thickness may bedetermined in the following manner. It is assumed that the cooler I be heated only by the radiation heat. Then the heat flux density is given by q 4.88 X 10' X I (t; 273)} lKtlll/ flhl (I) the high temperature arcs (5,000 l l,000C) are produced must be further taken into consideration, and the determination of the temperature of the atmosphere'in the furnace is very complex because the thermal conditions in the are furnace vary from time to time from the ignition stage, the boring stage, the stage of forming apool of molten metal, the melting stage and the refining stage. Therefore it is required to deter- According to the experiments conducted by the inventors the average temperature of the atmosphere in the furnace and combined coefficient I were found to be 1,600C and 0.35 1.0 in case of the conventional arc furnace operating at a conventional'power when the thermal load is highest so that the scrap covering the furnace wall is melted and the furnace wall is exposed. The combined coefficient is l.0;at the so-called hot spot which is directly exposed to the jet of the high temperature gas, but less than 1.0 at other spots. Therefore the coolers may sufficiently withstand the various thermal conditions in the furnace when the average temperature of the atmosphere in the furnace is taken as 1,600C and the combined coefficient, as l.0 when the coolers are designed. Substituting these data into equation (1), we have t 4\F(t,+ 2'73) q/4.88 X 10 X 1 273 4 (1600+ 273) q/4.88 X 10' X 1.0 273 (C) (2) From the relation between the thermal conductivity and thickness of the coolers which are dependent upon the material thereof,

l= t/q (2 -1,) [m] (3) where l= distance (m) from the surface of the cooling steel tube to the inner surface of the cooler;

A thermal conductivity (Kcal/mhC) of the main body of the cooler; and g V t temperature (C) of the cooling steel tubeat the surface thereof remote from the inner surface of the cooler. Thus, from equations (1 and (2) the thickness of the coolers may be determined.

For example when the temperature at the inner surface of the main body of the cooler with the thickness 1 mm which was made frOma special castiron having the high resistance to thermal fatigue was maintained less than l,l00C, the service life'of the cooler was over 1,000 heats. One of the factors which contributed to the elongation of the service life is the adhesion of the molten metal and slag to the coolers. That is, the molten metal and slag having the solidification points higher than the melting point of the main body 1 of the cooler form a protective wall or layer 3-10 mm in thickness over the inner surface of the cooler I and serve to lower'the temperature at the inner surface of the cooler I so that the service life'may be increased. Furthermore the protective layer serves to reduce the quantity of heat passing through the cooler so that the reduction in thermal efficiency of the cooler may be prevented. According to the experiments made by the inventors, the heat flux density of the conventional welded-steel jacket type cooler was6 X 10 Kcallm h at the maximum while the heat flux density of the cooler I with the relatively large dimensions was 100,000 Kcal/m h. It is seen that the thermal loss of the cooler of the present invention is very small- In case of the cooler l' a plurality of brick 5 are cast integral with the main body 1' so as to extend out of the inner surface of the cooler so that the adhesion of splash to the cooler may be facilitatedand the protective layer or wall may be formed. Therefore the quantity of heat passing through the cooler I may be re duced and the thermal loss may be minimized. According to the experiments conducted by the inventors, the heat flux density of the cooler I was of the order of 80,000 Kcallm h. The decrease in thermal efficiency of the furnace may be prevented and the thermal loss may be minimized so that the service life of the furnace wall may be increased. Since the cooling steel tubes 2 are cast integral with the main body 1', the problem of water leakage when the cracks are produced in the cooler may be overcome.

Since a plurality of cooling tubes 2 are cast'integral with the main'body 1 of the cooler I or I' so as to extend in the horizontal direction, the molten cooling tube or tubes may be disconnected from the cooling system even when a large quantity of molten metal and slag contacts with the cooler and melts its cooling tube or tubes. Therefore the coolers I and I used in the present invention may overcome the defects of the conventional cooler of the type having a plurality of vertically extending cooling tubes that the service life is shorter because the lower corner of the main body of the cooler which is subjected to a high thermal load is not sufficiently cooled; and the upper corner is also frequently damaged. Furthermore the coolers I and I may be used in the arc furnaces, and it is not required to lay brick in front of the cooler so that the maintenance and repair of the brick may be eliminated.

First Embodiment, FIG. 5

v In the furnace shown in FIG. 5 a cooler I of the type described with reference to FIGS. 1 and 2 is placed at the hot spot of a furnace wall 7 constructed by laying brick over a furnace bottom 6. The lower end of the cooler I is spaced apart from the surface of molten metal 8 by 200 500 mm so that molten metal 8 may not contact with the cooler I. The main body 1 of the cooler I is cooled by water passing through the cooling tubes 2 from the inlet 3 so that the refractory brick in Contact with the cooler I may be also cooled. Therefore the service life of the furnace wall may be increased and the efficiency of the furnace may be remarkably improved. Since the cooling tubes 2 are cast integral with the main body 1 of the cooler I, the water leakage problem may be overcome even when the cracks are produced in the cooler I. Furthermore the cooler I may prevent the local damage of the furnace wall so that the service life of the furnace may be further increased. Since the cooling tubes 2 are cast integral with the main body 1 so as to extend in the horizontal direction, the upper end of the cooler may be prevented from being damaged even when the brick are layed over the cooler I opposed to the conventional cooler.

In the furnace shown in FIG. 5 the cooler I is directly placed upon the bottom 6, but the cooler I' of the type shown in FIGS. 3 and 4 may be also used.

Second Embodiment, FIG. 6

The furnace wall of the furnace shown in FIG. 6 is constructed with the coolers I described with reference to FIGS. 1 and 2. Like the first embodiment, the lowermost coolers I are spaced apart from the surface of molten metal 8 by 200-500 mm so that molten metal may be prevented from contacting with the coolers I.

The coolers I are cooled by cooling water flowing through the cooling tubes 2 from the inlet 3 so that the furnace wall may be cooled. Therefore the service life of the furnace wall may become semipermanent. The coolers I may be removed from the furnace wall for maintenance and repair. Instead of the coolers I, the

damaged cooler may be replaced quickly with a new one. Fourth Embodiment, FIG. 8

The furnace shown in FIG. 8 has a polygonal cross sectional configuration. A plurality of coolers l are re movably laid over the bottom 6 as in the case of the third embodiment in such a manner that the furnace wall in opposed relation with the electrodes 9 are moved away therefrom. Fifth Embodiment, FIG. 9

The furnace shown in FIG. 9 is substantially similar in construction to the furnace shown in FIG. 8 except that it has a triangular cross sectional configuration.

In the furnaces shown in FIGS. 8 and 9, the coolers I are cooled by cooling water circulating through the cooling tubes 2 so that the furnace wall may be cooled.

Any damaged cooler may be removed from the furnace wall for repair or replacement, and the service life of the furnace wall may be increased.

In the steel making three-phase arc furnace, the arcs are generally directed toward the furnace wall under the electromagnetic forces so that the jet flows of the high-temperature gases are blown against the furnace wall. Therefore the scrap in opposed relation with the electrodes 9 may be quickly melted so that melting is not uniform. The portions of the furnace wall against which are directed the jet flows of high temperature gases are easily susceptible to damages (hot spot phenomenon), but in the embodiments shown in FIGS. 8

. and 9 the furnace wall in opposed relation with the electrodes 9 are moved away therefrom as far as possible so that scrap in the furnace may be uniformly melted.

Instead of the coolers I used in the furnaces shown in .FIGS. 8 and 9, any other suitable coolers for example the coolers I' shown in FIGS. 3 and 4 may be used. Sixth Embodiment, FIG. 10

The furnace shown in FIG. 10 is substantially similar in construction to the furnace shown in FIG. 6 except that the top of the furnace is converged. In addition to the advantages of the furnace shown in FIG. 6, the furnace shown in FIG. 10 has the following advantages:

i. The furnace roof may be made small so that the quantity of brick required for the construction of the furnace roof may be reduced. Therefore the cost of the furnace may be reduced.

ii. Since the furnace roof is small and light in weight, the capacity of the apparatus for lifting the furnace roof may be reduced.

iii. Melting of scrap may be facilitated, and bridge phenomenon may be eliminatd.

iv. Since the furnace is similar in configuration to a converter, oxygen blasting may become possible.

v. When the furnace is used as an arc furnace for melting reduced iron, reduced iron is gradually charged into the molten iron so that the so-called The furnaces shown in FIGS. 8 and 9 may also have i a converged top portion as the furnace shown in FIG. 10, and instead of the coolers 1, any other suitable coolers such as coolers I, any other shown in FIGS. 3 and 4 may be used.

So far the present invention has been described as being applied to'a steel making arc furnace, but it will be understood that the present invention may be applied to other furances and that the'furnace in accordance with the present invention may have any suitable cross sectional configuration in addition to the hexagonal and triangular cross sectional configurations shown in FIGS. 8 and 9. Furthermore in addition to the coolers I and I described above with reference to FIGS. 1-4, any other suitable cooler may be used. In the furnaces shown in FIGS. 7-10, all of the furnace wall is constructed with the coolers, but it will be understood that the coolers may be placed only at the hot spots as the furnace shown in FIG. 5.

The advantages of the furnaces of the present invention may be summarized as follows: A. Since the furnace wall is constructed with the coolers having cooling tubes cast integral therewith, and the cooling water is circulating through the cooling tubes, the water leakage may be prevented, the service life of the furnace wall may be increased, and the efficiency of the furnace may be remarkably improved, thus resulting in the reduction in cost. Since the inner surface of the cooler is so improved that the splash may easily adhere to the inner surface to form a protective wall or layer, the life of the furnace wall may be increased as the life of the coolers is increased.

B. Since the coolers are placed at the so-called hot spots of the furnace wall, the local damages may be prevented and the life of the furnace wall'may be increased.

C. Since the coolers are laid one upon another, all of the furnace wall may be cooled so that the life of the furnace wall becomes semipermanent. Therefore the efficiency of the furnace operation may be remarkably improved, thus resulting in the considerable reduction in cost. Y

D., Since the coolers may be easily replaced, the'time required for maintenance and repair may be reduced.

E. The cross sectional configuration of the furnace may be arbitrarily selected. Especially when the furnace is designed to have a polygonal cross sectional configuration so that the hot spots of the furnace wall in opposed relation with the electrodes may be spaced away from the electrodes, the scrap in the furnace'may be uniformly melted and the damage to the furnace wall may be minimized.

F. When the top of the furnace is converged, the dimensions and weight of the furnace roof maybe reduced so that the quantity of brick required for construction of the furnace roof may be reduced, thus resulting in the reduction in cost. Since the roof is light in weight, the capacity of the apparatus for lifting the roof may be reduced. The melting of scrap may be facilitated, and the consumption the roof brick may be minimized. v What is claimed is: 1. A furnace wall construction for metal heating furnaces, comprising I a. a furnace bottom wall (6) containing a cavity for receiving molten metal; and b. a furnace side wall (I) supported on said bottom wall above the level of the molten metal, said side wall including 1. at least one cast metal main body (4); and 2. a plurality of cooling tubes (2) cast integral with said main body or conducting a cooling fluid therethrough, each of said cooling tubes including horizontal portions contained in said main body, the internal surface of said main body being corrugated to define for each horizontal tube portion a convex surface arranged coaxially therewith, thereby to produce a uniform cooling effect on the side wall internal surface for permitting a protective layer of splash metal to be formed thereon. I 2. Apparatus as defined in claim 1, wherein-said side wall includes azplurality of said main bodies arranged at the hot spots of the furnace wall.

3. Apparatus as defined in claim 1, wherein said furnace side wall has a circular cross sectional configuration. 1 I

- 4. Apparatus as defined in claim 1, wherein said furnace side wall has a-polygonal cross sectional configuration.

5. Apparatus as defined in claim 1, wherein the top portion of the furnace converges to a reduced diameter.

6. Apparatus as defined in claim 1, wherein the thickness of each of said main bodies is so selected that the temperature at' the inner'surface of the main body is less than the melting point of the main body and the solidification point of the molten metal in the furnace.

7. Apparatus as defined in claim 1, wherein each of said main'bodies includes a plurality of bricks cast integrally on the internal surface thereof, the end surfaces of said brick being exposed at the inner surfaces of the sidewall. I 

1. A furnace wall construction for metal heating furnaces, comprising a. a furnace bottom wall (6) containing a cavity for receiving molten metal; and b. a furnace side wall (I) supported on said bottom wall above the level of the molten metal, said side wall including
 1. at least one cast metal main body (4); and
 2. a plurality of cooling tubes (2) cast integral with said main body or conducting a cooling fluid therethrough, each of said cooling tubes including horizontal portions contained in said main body, the internal surface of said main body being corrugated to define for each horizontal tube portion a convex surface arranged coaxially therewith, thereby to produce a uniform cooling effect on the side wall internal surface for permitting a protective layer of splash metal to be formed thereon.
 2. a plurality of cooling tubes (2) cast integral with said main body or conducting a cooling fluid therethrough, each of said cooling tubes including horizontal portions contained in said main body, the internal surface of said main body being corrugated to define for each horizontal tube portion a convex surface arranged coaxially therewith, thereby to produce a uniform cooling effect on the side wall internal surface for permitting a protective layer of splash metal to be formed thereon.
 2. Apparatus as defined in claim 1, wherein said side wall includes a plurality of said main bodies arranged at the hot spots of the furnace wall.
 3. Apparatus as defined in claim 1, wherein said furnace side wall has a circular cross sectional configuration.
 4. Apparatus as defined in claim 1, wherein said furnace side wall has a polygonal cross sectional configuration.
 5. Apparatus as defined in claim 1, wherein the top portion of the furnace converges to a reduced diameter.
 6. Apparatus as defined in claim 1, wherein the thickness of each of said main bodies is so selected that the temperature at the inner surface of the main body is less than the melting point of the main body and the solidification point of the molten metal in the furnace.
 7. Apparatus as defined in claim 1, wherein each of said main bodies includes a plurality of bricks cast integrally on the internal surface thereof, the end surfaces of said brick being exposed at the inner surfaces of the side wall. 